The present invention relates to a liquid ejection head in which the substantial length of a nozzle array for injecting a liquid is set to be as long as possible.
There has been known a liquid ejection head for injecting various kinds of liquid from a nozzle orifice. In particular, typical examples include a recording head to be mounted in an ink jet recording apparatus. Therefore, the related art will be described by taking the ink jet recording apparatus as an example.
As shown in FIG. 10, the ink jet recording apparatus 50 comprises a carriage 3 on which an ink cartridge 1 is mounted and to which a recording head 2 is attached.
The carriage 3 is connected to a stepping motor 5 through a timing belt 4, and is guided by a guide rod 6 and is reciprocated in the direction of the width of a recording medium 7 such as recording paper (primary scanning direction). The carriage 3 takes the shape of a box which is opened upward and is attached in such a manner that the nozzle formation surface of the recording head 2 is exposed to face the recording medium 7 (a lower surface in this example).
An ink is supplied from the ink cartridge 1 to the recording head 2 and an ink drop is discharged onto the upper surface of the recording medium 7 while moving the carriage 3, so that an image and a character are printed on the recording medium 7 in a dot matrix.
In order to guide the movement of the recording medium 7, there is provided a guide member 8 elongated in the primary scanning direction of the recording head 2. A wiper device 9 for cleaning a nozzle plate 17′ (which will be described below) of the recording head 2 and a capping device 10 for normalizing the viscous state of the ink in the nozzle orifice are provided adjacently to one end side of the guide member 8. A flushing box 11 having an opening 12 is provided adjacently to the other end side of the guide member 8.
A waste ink absorbed by the cleaning operation carried out by the capping device 10 and a waste ink discharged from the recording head 2 by the flushing operation with respect to the opening 12 are stored in a waste ink storage 13.
Although the ink jet recording apparatus 50 has been described as a part of the related art, it has such a structure that the liquid ejection head according to the invention can be mounted therein.
An ink ejection unit U′ included in the recording head 2 will be described with reference to FIGS. 11 to 13.
The ink ejection unit U′ is constituted by a head case 14′ and a channel unit 16′ fixed to a surface 15′ of the head case 14′ with an adhesive. The channel unit 16′ is constituted by laminating and bonding a nozzle plate 17, a channel forming substrate 18′ and a sealing plate 19′ also serving as a vibrating plate.
The nozzle plate 17′ is formed by a stainless plate, and is provided with a large number of nozzle orifices 20 to form two nozzle arrays 21. The channel forming substrate 18′ is formed by a monocrystalline silicon substrate and formed with pressure generating chambers 22 to be communicated with the nozzle orifices 20 and a damper concave portion 27 communicating with the atmosphere (not shown) which are formed by anisotropic etching. In the head case 14, an ink reservoir 23 communicating with an ink supply tube 26 is formed so as to communicate with the pressure generating chambers 22 through ink supply ports 25 formed in the sealing plate 19.
The sealing plate 19′ is formed by laminating a resin film and a stainless plate, and an island portion 19A of the stainless plate is formed on the back face of a portion corresponding to each of the pressure generating chambers 22. Moreover, there is formed a compliance portion 19C which is formed by only a resin film having almost the same contour as that of the ink reservoir 23 to be described below.
The head case 14′ is an injection molded product formed by a thermosetting resin or a thermoplastic resin, and is provided with the ink supply tube 26 for introducing ink to the ink reservoir 23. The damper concave portion 27 having an almost coincident shape with the shape of the ink reservoir 23 is formed in a portion of the channel forming substrate 18′ which corresponds to the ink reservoir 23.
Piezoelectric vibrators 30 are fixed on a fixing board 29 to form a piezoelectric violator unit 35 to be housed in a chamber 31. Each of the piezoelectric vibrators 30 is a vibrator element of longitudinal vibration mode which expands or contracts in its longitudinal direction in accordance with input of a drive signal to apply pressure fluctuation in the associated one of the pressure generating chamber 22.
The damper concave portion 27 is a space formed by the sealing plate 19′ for sealing an opening on the lower side of the ink reservoir 23 and a concave portion formed in the channel forming substrate 18, and serves to absorb pressure fluctuation in the ink reservoir 23 at time of the discharge of an ink drop by the deformation of the compliance portion 19C. During the deformation of the compliance portion 19C, air in the damper concave portion 27 is released from an air releasing hole (not shown) to the outside, thereby preventing pressure rising in the damper concave portion 27.
The ink ejection unit U′ having the structure described above is assembled in the following manner, for example. An adhesive is first applied onto the surface 15′ of the head case 14′ in order to prevent ink from flowing into the ink supply tube 26 and the chamber 31 or an adhesive sheet formed by punching to have a predetermined shape is stuck to the surface 15. The channel unit 16′ preassembled by bonding with an adhesive or the like is then mounted thereon. Subsequently, heating is carried out to have a temperature of approximately 40 to 100° C. and pressing is performed if necessary, thereby fixing the channel unit 16′ to the head case 14.
On the other hand, the piezoelectric vibrator unit 35 formed by fixing the piezoelectric vibrators 30 to the fixing board 29 is prepared and an adhesive is applied onto the tip ends of the piezoelectric vibrators 30. Next, the head case 14′ is inverted such that the channel unit 16′ faces downward. The piezoelectric vibrator unit 35 is accommodated in the chamber 31 and is bonded and fixed thereto. In this state, the tip ends of the piezoelectric vibrators 30 are bonded and fixed to the sealing plate 19′ of the channel unit 16′ and the fixing board 29 is finally fixed to the head case 14′ so that the ink ejection unit U′ is finished.
In the ink ejection unit U′, a driving signal generated in a driving circuit (not shown) is input to each of the piezoelectric vibrators 30 through a flexible cable 32, thereby expanding or contracting the piezoelectric vibrator 30. By the expansion and contraction of the piezoelectric vibrator 30, the island portion 19A of the sealing plate 19′ is vibrated to change pressure in the pressure generating chamber 22, thereby discharging ink in the pressure generating chamber 22 as an ink drop from the nozzle orifice 20.
The ink ejection unit U′ is attached to a plate-shaped head holder 33 through a coupling member 34. A pipe-shaped connector 36 is attached to the head holder 33 to lead ink from the ink cartridge 1 to the ink ejection unit U′. The connector 36 may be an ink supply needle (not shown) to pierce the inside of the ink cartridge 1 when the ink cartridge 1 is attached to the head holder 33.
A filter 37 is provided on the downstream side of the connector 36 and serves to catch impurities in the ink and to prevent the impurities from flowing into the ink supply tube 26.
Since the two nozzle arrays 21 are provided as described above, the pressure generating chambers 22, the ink reservoir 23 and the piezoelectric vibrator unit 35 are correspondingly arranged in two sets.
It is effective that the length of the nozzle array is elongated in a direction perpendicular to the primary scanning direction (hereinafter, referred as a secondary scanning direction) in order to enhance a printing speed, that is, increasing a printing area per unit time. In order to merely elongate the length of the nozzle array 21 in one ink ejection unit U′, however, it is necessary to maintain the relative positions among the nozzle orifices 20, the pressure generating chambers 22 and the piezoelectric vibrators 30 with high precision. Therefore, this method cannot be a proper measure.
As shown in FIG. 13C, the ink ejection units U may be arranged in the secondary scanning direction. However, the nozzle array 21 is not continuous so that a discontinuous interval L is formed.
The adherence relationship between the fixing board 29 and the chamber 31 is necessary for attaching the piezoelectric vibrator unit 35 into an accurate position. For this purpose, the end of the fixing board 29 is adhered to three internal walls 31X, 31Y and 31Z for positioning of the chamber 31 and a stopper wall 31D provided in an inserting direction so that the relative positions of the piezoelectric vibrators 30 and the pressure generating chambers 22 are maintained accurately. Since the fixing board 29 requires a predetermined width to fulfill such a positioning function, the total width of piezoelectric vibrators 30 in the direction of the nozzle array 21 is to be smaller than the width of the fixing board 29. At the same time, the thickness of the head case 14′ is also considered so that an interval L/2 is formed between the end of the ink ejection unit U′ and the end of the nozzle array 21 as shown in FIG. 13B.
In other words, the width of the fixing board 29 in the direction of the nozzle array 21 is set to be greater than length of the nozzle array 21. A difference between the lengths forms the interval L/2.
As shown in FIG. 14, the ink ejection unit U′ may be arranged in a zigzag manner to continuously provide each nozzle array 21 without the interval L viewed from the primary scanning direction, thereby substantially increasing the length of the nozzle array 21. In other words, the nozzle array 21 of each ink ejection unit U′ is continuously provided in a zigzag manner relative to the primary scanning direction, so that a long nozzle array having no break is formed relative to the secondary scanning direction. The ink ejection units U provided adjacently to each other have an overlapping array over a length corresponding to the interval L.
Even if a long nozzle array can be formed by the above configuration, since the width of the ink ejection unit U′ in the primary scanning direction is simply added, the dimension of the apparatus body in the primary scanning direction is remarkably increased so that the ink ejection head becomes large-sized. Moreover, since the stroke length of the carriage 3 in the primary scanning direction is determined such that the recording head 2 is wholly placed outside the recording region in which the recording medium 7 is placed, the added width of the recording head 2 causes disadvantages in view of the downsizing of the apparatus